Shaved is the past tense verb to shave, and it’s sometimes used as a past participle. Shaven is only used as a past participle. In other words, shaved is either a verb or an adjective, and shaven is an adjective. So English speakers are more likely to say “I have shaved” than “I have shaven.” But “his face is shaven” and “his face is shaved” both work.
Shave is one of a few irregular English verbs whose traditional participle forms no longer function as verbs. Others include melt (melted/molten), cleave (cleaved/cloven), and prove (proved/proven). The irregular past-participle forms of these verbs tend to fade away with time, and shaven likely won’t be around for long. As a past participle, shaved is already more common than shaven.
Examples
Rebels in Democratic Republic of Congo have kidnapped a Spanish doctor and shaved off all his body hair. [Reuters]
To my right, a man sat with shaven head and full-length earth-red robes. [Independent]
The BBC’s deputy political editor had his Movember moustache shaved off while filming a review of the political week. [BBC News]
The suspect is described as a clean-shaven, white male between 5’9″ and 6 feet tall. [Nashville Scene]